Ceramic protective coating composition



United States Patent 0 3,184,320 CERAMIC PROTECTIVE QOATIN'G CGWGSETKGNHarold J. Michael, Columbus, Ohio, assignor to North American Aviation,Inc. No Drawing. Filed Dec. 8, 1964, Ser. No. 416335 10 Claims. (Cl.196-43) The instant application is a continuation-impart of pendingapplication Serial No. 135,150, filed August 31, 1961, now abandoned.

This invention relates generally to ceramic protective coatings, andparticularly concerns ceramic protective coating compositions whichdevelop improved physical characteristics and improved performancecapabilities and which may be advantageously used to protect metalsurfaces and the like against oxidation and corrosion, especially atelevated temperatures.

The invention disclosed and claimed herein involves a ceramic protectivecoating which is essentially comprised of a refractory and threeseparately formulated hightemperature glass frits having prescribedchemical (although not necessarily composition) characteristics, suchconstituents being combined in preferred proportions. The threeseparately formulated glass frits are further individually selectedaccording to certain physical properties and are basically characterizedin this respect as having a low thermal expansion characteristic, amedium thermal expansion characteristic, and a high thermal expansioncharacteristic, respectively. The ceramic protective coating of thisinvention may be modified by the proper addition of a metal to developan improved resistance to spalling characteristic. Also, the ceramicprotective coating of this invention may be modified by the addition ofcertain oxides to selectively improve other specific physical andperformance characteristics.

As used in this application, the term low thermal expansion glass frit(and similar terms) refers to a hightemperature glass frit materialhaving a coefiicient of thermal expansion in the approximate range offrom 3 10 to 5x10" inches per inch per degree Fahrenheit. The termmedium thermal expansion glass frit (and like terms) are used in thisapplication to reference a hightemperature glass frit material which hasa coeflicient of thermal expansion in the approximate range of from 5 X10- to 7 X10 inches per inch per degree Fahrenheit. The term highthermal expansion glass frit refers to a high-temperature glass frithaving a coefficient of thermal expansion in the approximate range offrom 7 1t) to '10 10 inches per inch per degree Fahrenheit.

An important object of this invention is to provide a ceramic protectivecoating which includes separately formulated high-temperature glassfrits, each having the desired chemical characteristics and furtherhaving a low, medium, and high thermal expansion characteristic,respectively, combined in proper proportions to develop an improvedthermal expansion characteristic match as to metal surfaces to which thecoating is applied.

Another important object of this invention is to provide a ceramicprotective coating which includes separately formulated high-temperatureglass frits, each having the desired chemical characteristics andfurther having a low, medium, and high thermal expansion characteristic,respectively, combined in proper proportions to develop improvedresistance to failure by thermal shock.

Another object of this invention is to provide a ceramic 3,l84,32fiPatented May 18, 1965 protective coating which includes separatelyformulated high-temperature glass frits, each having the desiredchemical characteristics and further having a low, medium, and highthermal expansion characteristic, respectively, combined in properproportion to develop improved adhesion to metal surfaces particularlymetal surfaces treated with nickel and chromium or chromium-containingalloys.

Another object of this invention is to provide a ceramic protectivecoating which includes separately formulated high-temperature glassfrits, each having the desired chemical characteristics and furtherhaving a low, medium, and high thermal expansion characteristic,respectively, combined in proper proportions to develop an improvedthermal endurance capability at elevated temperatures.

Another object of this invention is to provide a ceramic protectivecoating which includes separately formulated high-temperature glassfrits, each having the desired chemical characteristics and furtherhaving a low, medium, and high thermal expansion characteristic,respectively, combnied in proper proportions, and which may be readilymodified by inclusion of a metal additive to develop improved resistanceto spalling caused by bending or torsion.

Another object of this invention is to provide a ceramic protectivecoating which includes separately formulated high-temperature glassfrits, each having the desired chemical characteristics and furtherhaving a low, medium, and high thermal expansion characteristic,respectively, combined in proper proportions, which may be readilymodified by the inclusion of a metal additive to develop improvedresistance to spalling caused by thermal and mechanical stresses.

Another object of this invention is to provide a ceramic protectivecoating which includes separately formulated high-temperature glassfrits, each having the desired chemical characteristics and furtherhaving a low, medium, and high thermal expansion characteristic,respectively, combined in proper proportions to develop reduced porosityand increased protection capability against oxidation and corrosion,especially at elevated temperatures.

A still further object of this invention is to provide a ceramicprotective coating which includes separately formulated high-temperatureglass frits, each having the desired chemical characteristics andfurther having a low, medium, and high thermal expansion characteristic,respectively, combined in proper proportions to develop an improveddielectric property.

Another object of this invention is to provide a ceramic protectivecoating which includes separately formulated high-temperature glassfrits, each having the desired chemical characteristics and furtherhaving a low, medium, and high thermal expansion characteristic,respectively, combined in proper proportions, and which may be readilymodified by the inclusion of a suitable oxide to adjust thermalexpansion, refractoriness, and other coating physical properties.

The ceramic protective coating of this invention also obtains importantadvantages as to resistance to chemical attack, ease of application tometal surfaces, maintainability, and economy.

Other objects and advantages of this invention will become apparentduring consideration of the following description.

APPLICATION The ceramic protective coating invention described hereinhas particular utility with respect to products corrosion-causingconstituents, such corrosion-resistantalloys are generally subject toand/ or corrosion.

The ceramic protective coating invention described herein also hasutility with respect to parts fabricated'of appreciable oxidation steel,iron, copper, or certain exotic metals, and to temperature-resistantparts fabricated of graphite and the like having a subsequently appliedoxidation-susceptible metal surface, if the to-be-protected surfaceareas of each such part is provided with a proper intermediate film todevelop improved coating adhesion. In "general, such intermediate filminvolves the application of an overlay comprised essentially of nickeland chromium to the part in, contacting and adhering relation to,to-be-protected surface areas, In the event that environmenttemperatures which are only intermediate in'magnitude are anticipated asto theto-be-coated part (temperatures of from approximately 900 F. toapproximately 1500 F.), the.

overlay may be comprised essentially only of chromium. Detailsregarding'methods for developin the necessary intermediate .film onoxidation and corrosion-susceptible surfaces are provided in theabove-referenced co-pending application and also in my co-pendingapplication Serial 'No. 108,263, filed May 8, 1961.

Numerous dhferent parts have been provided with the ceramic protectivecoating of this invention. Such parts include quartz lamp reflectorsfabricated of Type 321 stainless steel, a sliding surface clamp employedin a high; performance aircraft air 'conditioning system andfabricated'of Type 304 stainless steel, support grid brazingCorrosion-resistant alloys At temperatures from approxiof theto-be-processed part. As an alternate, fused alumina grit ranging fromNo. 60 mesh to No. 321 mesh may be substituted for sand; It is preferredthat the air blast delivery pressure he kept to a minimum to avoidwarpage when abrading thin, light-Weight, or sheet-like base materials.i

If component parts fabricated of thin, sheet-like corrosion-resistantalloys'cannot be subjected to the abovedescribed abrading process or toan equivalent abrading operation, a conventional acid pickling oretching technique may be employed as a substitute procedure.

In the event the ceramic protective coating invention described hereinis to be applied to component parts having surfaces which are readilysusceptible to oxidation and corrosion at temperatures of fromapproximately 900 F. upwards, his only necessary tovclean and abrade theto-be-coated surface areas .prior to application of, the

, overlay film. referenced above.

fixtures fabricated of Inconel and used in retorts for overlay todevelopimproved resistance to corrosion at 7 intermediate and elevatedtemperatures are provided in the above-referenced copendingapplications.

PRE-TREATME T It is recommended that the metal surfaces of the componentparts to be processed in accordance with this invention be pretreated bysuitable cleaning and abrading. Surfaces having oils or lubricantspresent thereon are preferably cleaned utilizing conventional solventmaterials, or vapor degreasing technigues, or emulsion cleaning agents.If only very light oils or fingerprints are present on the metalsurface, cleaning may be accomplished using known commercial alkalinecleaners. Afterwards, the part should be rinsed and dried.

It is also recommended that the cleaned metal surface then be abradedusing conventional abrasives. ing may be accomplished by delivering No.40 mesh Sand blast sharp sand by air blast at approximately to 120pounds per square inch air pressure uniformly over the surface PROCESSSTEPS slip to the base part by firing to maturity.

The ceramic protectivecoating of this. invention is basically comprisedof three separately, formulated high-temperature glass frits, eachhaving thedesired chemical characteristics and further having a low,medium, and high thermal expansion characteristic, respectively,combinedin proper proportions andwith a refractory oxide. The ceramic protectivecoating of this invention typically also includes a clay or clay-likesuspension agent whichmateriallyfacilitates applicationof the coatingwhen it is mixed with sufficient Water to form asuitable slip. Thehereinafter detailed'coating slip is preferably dried after applicationto the to-be-protected surfaces and before firing; it is preferablyprovided on the part to a depth which will result in a final firedceramic protective coating thickness of 0.001" to 0.002". V

The applied coating is afterwards fused to the base part'to-be-protected surfacesby furnace firing in an air atmosphere attemperatures of from approximately 1700 F.

to, 2200 F. The firing schedule actually selected depends upon theparticular compositionof the coating material. Conventional furnaceequipment and firing practices are employed to carry out the coatingfiring operation.

Detailed information with respect to the composition of the ceramicprotective coatingof. this invention is provided in the descriptionwhich follows. In generaLthe coating composition may be modified Withinlimits to meetvthe requirements of particular applications- Coatingcharacteristics relating to required application technique, firingtemperature, flow property, and the like may be developed or adjustedusing formulation techniques which are generally known to those skilledin the art.

CERAMIC PROTECTIVE COATING COMPOSITION The glass frit-refractoryprotective coating which comprises this invention may be developedthrough use of a sliphaving, by weight: I I

. j e V 7 Parts Mixed glass frits Refractory oxide 2-100 Suspensionagent Q /z--10 Water 407 0 to the amount of refractory materialcontained in the glass frit. Detailed information will be providedhereinafter with respect to the glass frit, refractory oxide, andsuspension agent portions of the above-indicated protective coatingslip. Such information will establish a better understanding as to thehigh-temperature glass frit-refractory type of ceramic coatings which Ipreferably employ in the practice of this invention.

(I) Glass frits The high-temperature glass frits which are separatelyformulated and employed in the practice of this invention are selectedfor their chemical characteristics of being both fluorine-free and oflow (or zero) alkali metal oxide content and each include, incombination, glass-forming ingredients and a refractory additive. Asused in this application, the terms low alkalinity" and low alkali metaloxide content relate to a glass frit wherein the total alkali metaloxides included in the composition is less than approximately 12% on aparts by weight basis. Each separately formulated glass frit is alsocompounded to provide, in addition to such chemical characteristics,controlled physical properties relating to softening point temperature,fusion flow, and thermal expansion coeflicient. As previously suggested,the separately formulated glass frits employed in the practice of thisinvention are identified in terms of a thermal expansion coefiicientthat may be categorized as low, medium, or high in comparative value,respectively. Such identifications are primarily for convenience.Formulation details regarding so-identified glass frits considered asrepresentative to the practice of this invention are provided in theExample G, Example H and Example 1' glass frit compositions whichfollow.

As to prescribed control of the required physical properties for thehigh-temperature glass frits utilized in the practice of this invention,additional comments are helpful. First, such frits must each have asoftening point temperature which is in the range of approximately 1100"F. to 1250 F. Different temperatures occur within that range as aconsequence of the different specific formulations involved in thepractice of the invention. Such temperature values have been determinedby use of an automatic recording thermal expansion dilatometer inaccordance with conventional laboratory practice while heating thespecimen glass over a range from room temperature to the softening ordeformation point.

Second, in controlling the fusion flow property of the differenthigh-temperature glass frits, attention must be given to the manner ofmeasuring that property. Basically, the following technique is adoptedas the standard for the measurement. A standard gram dry sample of theglass frit is crushed to pass a 40 mesh screen and to remain upon an 80mesh screen. The sample is mixed with a small quantity of organic binderand diluent sufficient to develop a cohesive shape when prepared in acylindrical die of 1" diameter using approximately 2,000 pounds persquare inch pressure. The resulting prepared 1" diameter button isdried, placed upon a stainless steel panel (approximately 4" x 4" x0.050), and fired at 1800 F. for minutes allowing the specimen to fuseand flow. The fired and flowed frit button is subsequently cooled toroom temperature to solidify. The degree of fiow of the fired frit ismeasured on the basis of the ratio of the diameter of the flowedmaterial to the original button diameter but preferably is expressed asa percentage excess over 100%. Thus, a 1" diameter button having anaverage fired and solidified diameter of 1 /2 has a diameter ratio of1.5 (150%) and fusion flow value of 50%. The flowed dimensions areestablished as the average of two dimensions taken at right angles toeach other. The high-temperature glass frits indicated herein as havinglow, medium, and high thermal expansion coefiicient characteristics arerequired to have such fusion flow values in the ragnes given below inorder for the effective practice of this invention:

Frit thermal expansion Fusion flow characteristic identification: value,percent Low 7-22 Medium 38-48 High -75 The thermal expansion coeflicientproperty selected for each of the required separately formulatedhigh-temperature glass frits should fall within the different rangesdetailed in the introduction portion of the instant specification.Basically, the frits should each be Within a different one of the rangesgiven below:

Frit thermal expansion characteristic identification: Value range Low3-5 Medium 5-7 High 7-10 The above values are expressed in terms of 10"inches per inch per degree Fahrenheit.

A representative cross-section of refractory oxide additives which maybe combined with the glass-forming ingredients to establish a suitablefrit inclues the oxides of: nickel, chromium, aluminum, silicon,titanium, zirconium, iron, manganese, molybdenum, cobalt, cerium,niobium, vanadium, and tin. The percent weight of refractory additivedepends upon the degree of solubility of the particular oxide in thebasic glass system. For example, the oxides of titanium, iron,manganese, and niobium are comparatively soluble in the glass andfunction to add thermal endurance qualities to the protective coatingwithout developing excessive refractoriness. The oxides of cerium andcobalt are moderately soluble in the basic glass and cannot be added inlarge quantities without effecting a loss of flow. The oxides of nickel,chromium, aluminum, and zirconium are least soluble in the glass andsmall quantity additions thereof operate to develop refractoriness, heatresistance, and reduced flow characteristics in the resulting glassfrit. Although the above-discussed oxides may be employed to adjustbasic physical charactersitics, for simplification purposes it ispreferred that the oxide of aluminum alone be used as the fritrefractory additive.

In the following frit examples A1 0 only is the glass frit refractoryoxide additive; silica is used in each glass frit formulation as aglass-forming ingredient. Specific oxide combinations which developglass frits having a desired individual high, medium, or low thermalexpansion characteristic are disclosed in the following Example G, H,and J formulations, respectively.

EXAMPLE G.-GLASS FRIT COMPOSITION [Parts by Weight] Ingredient RangePreferred amount EXAMPLE H.GLASS FRIT COMPOSITION [Parts by weight]Ingredient Range Preferred amount EXAMPLE .T.GLASS FRlDCOMPOSITION[Parts by weight] Ingredient Range Preferred amount SiOz 77. -84. 0 81.0203 9. 0-17. 0 13. 0 V 2. 0- 5. 0 3. 8 1. 0- 3. 0 2. 2

Batching ingredients for the above different frit oxide compositions aregiven below.

The preferred high thermal expansion glass frit composition set forth asExample G may be developed by smelting the following glass frit batchingingredients in the indicated amounts by weight at 2500 F. to 2650 F.until free of bubbles and afterwards quenching the molten composition:

i i Parts Silica .Q' 426.0 Barium carbonate 341.0 Potassium 91.5 Zincoxide 80.0 Boricoxide 35.5 Soda ash (anhydrous) 15I0 Aluminum hydrate .i11.0

' the indicated amounts by weight at 2500 F. to 2650 F.

until free of bubbles and afterwards quenching the molten The softeningpoint temperature of this material is approximately 12717" .F. Thecoefficient of thermal 'expansion for this Example H-Glass Frit isapproximately 6.8 inches per inch per degree Fahrenheit measured overthe range of room temperature to softening point. Fusion flow value forthis particular] frit was determined to be 43.8%.

The preferred low thermal expansion glass fit composition set forth asExample I may be developed by smelting thefollowing glass frit batchingingredients in the indicated amounts by weight at 2500 F. to 2650 F.until free of bubbles and afterwards quenching the molten composition: t

a Parts Silica h 752.0 Nepheline-syenite 93.0 Anhydrous borax 80.0 Boricoxide 75.0

ever, smelting equipment for the higher'temperature is not alwaysavailable. '7 V The above preferred glass frit compositions areconsidered as representative of the formulations that would :be resortedto or used by develop the glass frit properties and characteristics re-8 v persons skilled in the art to 'quired by the practice of thisinvention. Again, each of the necessary high-temperature ,glass fritsmust chemically be free of fluorine and must have a low (or Zero)alkalinity. Each of the required frits must have a softening pointtemperature in the range ofapproximately 1100 F. to 1250 F. The threedifferent required hightemperature glass frits must have fusion flowvalues, as measured by the hereinbefore detailed procedures, in theranges of 7% to 21%, 38% to 48%, and 60% to 75% for the low, medium, andhigh thermal'expansion coefiicient characteristic identifications,respectively. 7 As to the thermal expansioncharacteristics of thedifferent frits, the ranges of 3 to 5, 5 to 7, and 7' to 10 for thermalexpansion coefiicients based on 1 0 inches per inch per degree 'ditio'nto the ceramic protective'coat'ing slip is generally comprised of one ormore of the refractory oxides identiface of the processed product.

composition: I

. a 7 Parts .Barium carbonate 480.0 Silica i 356.0 Zinc oxide g V 380.0Boric oxide 53.0 Aluminum hydrate 31.0

Fahrenheit should apply to the low,'medium, and high characteristiccategories, respectively. Other known com positions for glass frits willproduce equivalent properties and will function in this invention in themanner of the detailed formulations. Accordingly, the above glass fritcharacteristics and not primarily on the basis of formula- (II)Refractory oxide The refractory material selected and used as a milladfied above in connection with the description of the glass fritrefractory additive. The refractorymaterial is milladded to the sliptoproduce the desired firing tempera- "ture, maturing temperature, andcoefiicient of thermal expansion-contraction to "fit the base metal ormetal sur- The amount of refractory oxide included in the slipcomposition depends upon the 'refractoriness of the glass frit used inthe slip. For instance; a comparatively high percentage of refractory'oxide melted into the basic glass increases the frit meltingtemperature, reduces its fiow characteristics at the maturingtemperature desired, and would be used with relatively less additionalrefractory, if ,any, in the slip sufficient flow is developed duringfiring to completely eliminate coating porosity within the first two orthree minutes of the iiring operation. 7'

The following refractory oxide additive is essentially only a' mixtureof refractory oxides and may be employed advantageously in the ceramicprotective coating slip formulation which is hereinafter described inconnection with an Example L slip formulation. 'For identificationpurposes, this particular refractory oxide mixture is designated ExampleK and has thefollowing composition:

EXAM E KREFRACTORY J V [Parts by weight] 7 Ingredients: 7 Preferredamount h c'rgog V (III) Suspension agent The above-identified glass sliptypically includes a suspension agcnt to maintain proper dispersion ofthe glass frits and refractory oxide in either a water or oil vehicle.It is generally preferred that either enamelers clay or bentonite beused as a suspension agent in connection with this invention. Normally,a relatively lesser quantity of bentonite is required if such is used inplace of enamelers clay. A good grade of purified bentonite, as commonlyused with porcelain enamel materials is recommended. If enamelers clayis employed, a water-washed, air-floated enamelers grade of clay havingmoderate to high set is preferred.

(IV) Slip formulations The descriptive information which followsprovides details with respect to three different ceramic protectivecoatings which each incorporate the features of this invention. Theditferent coating compositions are designated as Example L, Example M,and Example N coating. Each composition is described by a slipformulation and includes separately formulated glass frits having a low,a medium, and a high thermal expansion characteristic, respectively, anda refractory additive. The three different coating compositions aresuited to different applications. From the standpoint of application tocorrosion-resistant alloy parts and steel or iron-like parts coated withan intermediate adhesion-improving overlay, the slip formulationsdisclosed by Example L have found greatest use. The various slipformulations which may be developed within the limits set forth inExample L are each characterized as having a medium thermal expansioncharacteristic for the composite ceramic protective coating. Details forformulating ceramic protecting coating slips which may be applied andfired to maturity to develop protective coatings having a high thermalexpansion characteristic or a low thermal expansion characteristic areprovided in Examples M and N, respectively. The formulations suggestedby Example M have found application to component parts made of copperand copper alloys provided with the previously-discussed intermediateoverlay. The slip formulation suggested by Example N have foundapplication to component parts made of graphite and provided with anintermediate, readily oxidizable metal surface that is protected by asuitable chromium and nickel overlay. The mill formulations fordeveloping Examples L, M, and N coating slips are as follows:

EXAMPLE L.PROTEOTIVE COATING SLIP The above-listed slip batchingingredients are preferably milled to a trace on a 325 mesh screen(relative to a 100 gram sample) prior to application.

EXAMPLE M.PROTECTIVE COATIN G SLIP [Parts by weight] Ingredients RangePreferred amount Low thermal expansion glass frit 35. -40. 0 37. Mediumthermal expansion glass frit. 10. 0-15. 0 12. 5 High thermal expansionglass frit 35. 0-50. 0 37.5 Titanium dioxide 5. 0-20. 0 10.0 Nickelmonoxide 2. 0- 3. O 2. 5 Chromic oxide 2. 0- 3. 0 2. 5 Annealed nickelpowder 5 mesh) 7. 0- 8. 0 7. 5 Enamelers clay 3. 0-10. 0 5. 0 Distilledwater 30. 0-70. 0 (i0. 0

ing a reduced thermal expansion coefiicient.

The slip ingredients listed above in connection with Examples M and Nare milled in the manner of the slip ingredients identified inconnection with Example L. The preferred amounts of Low, Medium, andHigh Thermal Expansion Frits indicated in connection with Examples L, M,and N formulations given above are based specifically on the Examples J.H, and G glass frit compositions prevously detailed.

In the Example M protective coating slip the refractory oxide portion iscomprised of titanium dioxide, nickel monoxide, and chromic oxide.Nickel monoxide and chromic oxide are included in the composition todevelop increased refractoriness and an increased thermal expansioncoefficient in the resultant coating. Aluminum oxide, if added to theceramic coating, would perform a similar function. Titanium dioxide isincluded in the composition to develop increased thermal expansionwithout increasing the refractoriness quality of the material. Therefractory oxide ceria may also be used to achieve the function oftitanium dioxide.

In the Example N protective coating slip silica is included as therefractory oxide to develop a coating hav- Zinc oxide may be used todevelop a similar low thermal expansion characteristic withoutincreasing the refractoriness quality of the coating.

Each of the slip formulations given above indicates that powdered nickelis included as an additive. Such material, as is well-known in the art,functions to develop increased resistance to spalling caused bymechanical or thermal stresses. In practicing my invention I prefer thatthe powdered nickel metal additives be annealed and reduced to 325 mesh.Metal powder particles should not be in excess of 74 microns in particlesize.

Another suitable high thermal expansion glass frit which has been usedin the practice of this invention is comprised of 61.4 parts (by weight)of lead oxide (PbO) smelted with 7.1 parts of aluminum oxide (A1 0 and31.5 parts of silicon dioxide (SiO This particular frit has acoefficient of thermal expansion of 8.1 x 10- inches per inch per degreeFahrenheit and is particularly useful in slip formulations having acomparatively large proportion of low expansion glass frit to improvefiring fluidity and thereby minimize resulting pinholes.

The above examples establish that the ceramic protective coating of thisinvention preferably includes separately formulated frits andrefractory, together with a suitable suspension agent and water forfacilitating application, combined in the following ratio:

Ingredient Range Low thermal expansion glass frit 35.0-80.0 Mediumthermal expansion glass frit 10.0-1 5.0 High thermal expansion glassfrit 10.0-50.0 Refractory oxides 9.0-26.0

The range given is on a parts by weight basis. To formulate a suitableslip, from 3 to 10 parts suspension agent and from 50 to 70 parts waterare added to the basic coating ingredients. It is believed that thepreferred limits with respect to incorporated refractorp oxide,suspension agent, and water may be extended somewhat to also obtainimproved results in certain specific applications.

i i APPLICATION EXAMPLES The ceramic protective coating invention ofthis application has been utilized in numerous instances to produce newand unexpected results in terms of coatingv performance. The advantagesassociated with the claimed coating composition relate to such qualitiesas thermal' endurance at elevated temperatures, improved adhesion tounderlying nickel-chromium metals, high resistance to failure caused bythermal shock, resistance to spalling caused by bending, torsion, orthermal stress, improved,

dielectric properties, and the like. Examples of specific uses of thecomposition are given below.

A clamp component fabricated of Type 321 stainless steel andmanufactured for use in a high-performance aircraft conditioning systemwas first cleaned and abraded in accordance with the procedures outlinedunder. the heading Pro-Treatment. The clamp component, which was made of0.040 thick material, wascoatedwith asufiicient quantity of thepreferred protective coating slip of Example L 'to produce a firedthickness of approximately 0.002". at 1800? F. for seven minutes todevelop coating maturity.

for the coating ranged from 85 to 100%. of the coating to thicknesses upto 0.003" are capable of resisting 360 torsion stresses .(on 0.040"thick metal) using the standard Porcelain Enameling Institute torsionExample L. Application of the-coating slipto thepart was by a sprayingtechnique and included the covering of weld join-ts. The applied slip,after suitabledrying,

The coated parts were subjected to ten repeated cycles wherein each partwas heated to a temperature of 1700 F. to 1750 F; and immediatelyquenched in tap water at room temperature. In addition, the parts werecontinuously maintained in an air atmosphere at a temperature of atleast 11700 F. for over 1,000 hours. There was no detectable failure ofthejhigh-temperature ceramic protective coating and no corrosion oroxidation of the base metal protected thereby. The best knownconventional ceramic protective coating. applied to such parts was,capableof less than 100 hours endurance 'at' the 1700 F. temperature. I

The preferred coating of Example L was also applied to hanger bracketsmounted in a steam boiler for supporting tube components. Such hangerbrackets were fabricatedof east Series 400 stainless steel. ferredceramic protective coating composition-of Example L was applied to athickness of approximately 0.002" and fired to maturity at1800 F. over a35 minute period. The extended firing period was necessitated by themass of the bracket casting. After several months use in connection withnormal boiler operation, the coated bracket was inspected and observedto not have suffered any surface deterioration of coating or metal. Astateof-the-art .ceramicprotective coating applied to the same ExampleM'to include the preferred amountsof Exann.

ples J, H, and G glass frits has been utilized advantageously inconnection with the protection of copper bars.-.

The coated bar was first provided with proper .abrading The specificallypreferred slip was fired In subsequent tests it was determined that "thePorcelain Enameling Institute adherence method index 7 Applications Thespecific composition employed corresponded to the pre-" ferred specificformulation given in connection with.

The pre '40 was fired to maturity at a temperature of 1800 F. to.

and cleaning pro-treatment and was also provided withsequentially'applied nickel and chromium'strikes to a total depth ofapproximately 0.0003". The slip was applied to the prepared copper barto develop a coating thickness of 0.001" to 0.002" after firing the slipto maturity at 1800" F.

The so-coated copper bar was subjected to four repeated cycles whereinthe part was heated to a temperature of 1S50 F. for one-half hourandafterwards quenched in tap water at room temperature; The improvednon-porous protective coating exhibited no failtire with respect toeither porosity or adhesion. In addiion, the copper 'part exhibited nocorrosion or oxidation due to the air atmosphere in which it was heated.The coating andmetal part exhibited no deterioration after exposure toan air-containing environment for 10.0 hours at 1500 F. 1

I claim: 7 1. A ceramic protective coating composition consisting of:

(a) From 2% to 50% by weight of refractory oxide selected from the groupconsisting of the oxides of aluminum, cerium, chromium, cobalt, iron,manga- V nese, molybdenum, nickel,-niobium, silicon, tin, ti-

tanium, and vanadium, and p '(b) The balance a mixture of glassfrits'whic. each are fluorine-free and of less than 12% alkali metaloxide content by weight, which each are separately fritted, and whichconsists on a weight basis of: I p

- (1)' 35 to 80- parts of a first, glass frit having a softeningtemperature in the range of 1100 F.

to 1250 F having a fusion'flow value in the range of 7% to 22%, andhaving a thermal expansion coefiicient iii-the range 3 10 to 5 10 inchesper inch per degree. Fahrenheit, (2) to' parts of a second glass frithaving a softening temperature in the range of 1100 F. .to 1250 'F.,having a' fusion flow value in the range of 38% to148%, and having athermal expansion coefficient in the range of 5x10" to 7 10- inches perinch per degree Fahrenheit,

and p ('3) .10 to 50' parts of a third glass frit-having a I softeningtemperature in the range of 1100 F. 4 to,1250 F., having a fusionflowvalue in the range of 60% to 75%, and having a thermal expansioncoefficient in the range of 7X10 to 1,0)(10- inches per inch per degreeFahrenheit.

2. The ceramic protective coating, compositiondefined by claim 1,wherein said mixture of glass frits consists of: 50 to 80 parts of-saidfirst glass frit, 10 to 15 parts of said second glass frit, and 10to 15'parts of said third glass frit. r v

3. The ceramic protective coating composition defined by claim 1,wherein said mixture of glass frits consists of to parts of said firstglassfrit, 10 to 15 parts of said second. glass frit, and 35 to 40 partsof said third glass frit.

4. The ceramic protective coating composition defined by claim 1,wherein said mixture of glass frits consists of: 35 to -40 parts'ofsaid'first' glass frit, 10 to 15 parts of said second glassfr'it, and 35to parts of' said third glass frit. j

5. The ceramic protective coating composition defined by claim 1,wherein there is alsolincluded an additive,

said additive consisting of 7 to 8 parts by'weight of an-.

nealed nickel in fine powder form. p

6. The ceramic protectivecoating composition defined byclaim 1, whereinsaid mixture of glass frits consists of: approximately parts of'saidfirst glass frit, approximately 12.5 parts of said second glass frit,and approxi: mately 12.5 parts of said third glass frit.

by claim 4, wherein said refractory oxide consists of titanium dioxide,chromic oxide, and nickel monoxide.

References Cited by the Examiner UNITED STATES PATENTS Long 10648 Long10648 Long et a1. 106-48 Long et a1. 106-48 Larsh et al. 106-48 Michael106-48 TOBIAS E. LEVOW. Primary Examiner.

1. A CERAMIC PROTECTIVE COATING COMPOSITION CONSISTING OF: (A) FROM 2%TO 50% BY WEIGHT OF REFRACTORY OXIDE SELECTED FROM THE GROUP CONSISTINGOF THE OXIDES OF ALUMINUM, CERIUM, CHROMIUM, COBALT,IRON, MANGANESE,MOLYBDENUM, NICKEL, NIOBIUM, SILICON, TIN,TITANIUM, AND VANADIUM, AND(B) THE BALANCE A MIXTURE OF GLASS FRITS WHICH EACH ARE FLUORINE-FREEAND OF LESS THAN 12% ALKALI METAL OXIDE CONTENT BY WEIGHT, WHICH EACHARE SEPARATELY FRITTED, AND WHICH CONSISTS ON A WEIGHT BASIS OF: (1) 35TO 80 PARTS OF A FIRST GLASS FRIT HAVING A SOFTENING TEMPERATURE IN THERANGE OF 1100*F. TO 1250*F., HAVING A FUSION FLOW VALUE IN THE RANGE OF7% TO 22%, AND HAVING A THERMAL EXPANSION COEFFICIENT IN THE RANGE3X10-6 TO 5X10**-6 INCHES PER INCH PER DEGREE FAHRENHEIT, (2) 10 TO 15PARTS OF A SECOND GLASS FRIT HAVING A SOFTENING TEMPERATURE IN THE RANGEOF 1100*F. TO 1250*F., HAVING A FUSION FLOW VALUE IN THE RANGE OF 38% T48%, AND HAVING A THERMAL EXPANSION COEFFICIENT IN THE RANGE OF 5X10-6TO 7X10**-6 INCHES PER INCH PER DEGREE FAHRENHEIT, AND (3) 10 TO 50PARTS OF A THIRD GLASS FRIT HAVING A SOFTENING TEMPERATURE IN THE RANGEOF 1100*F. TO 1250*F., HAVING A FUSION FLOW VALUE IN THE RANGE OF 60% TO75%, AND HAVING A THERMAL EXPANSION COEFFICIENT IN THE RANGE OF 7X10**-6TO 10X10**-6 INCHES PER INCH PER DEGREE FAHRENHEIT